From 1999 to 2001, AMG would, for those customers with the financial capability and desire to have something truly special, bore out the wondrous 6.0-litre M120 V-12 engine in the SL600 to 7.3-litres, upgrade the internals, and unlock in the region of 520 horsepower and 550 pound-feet of torque. Thankfully, the brakes and active damping system were also fettled to cope with the extra power, and the result was a traction-restricted 0–60 time of 4.6 seconds and a top speed approaching 200 mph. In keeping with the understated gentlemanly appearance of the R129, the only items that give away its potency are the twin exhaust, a discreet body kit, small exterior badging, and AMG wheels.

Just 85 examples of the SL 73 were reportedly produced during the model’s three year availability, during which AMG also sold a similar quantity of engines to the Italian manufacturer Pagani for use in their Zonda. By 2002, Pagani had begun fitting the 7.3-liter V-12 borrowed from the SL 73, and this notable arrangement would continue for every naturally aspirated Pagani chassis until 2017.

This 1999 SL 73 example is clad in Green Black Metallic over black leather with burl trim and a black convertible soft top; a matching auxiliary hardtop is included. The gauge cluster offers the only hint that something unique lies beneath the hood—a large AMG logo is centrally affixed to the 300 kph speedometer. Because the SL 73 is in truth a modified SL 600, it is still presented wearing all the refined finishes of the stock convertible--nearly every surface is clothed in black leather, including the upper dashboard fascia and even the anti-roll bar. A six-disc CD changer is nestled in the car’s trunk, and a factory provided Nokia mobile phone is still mounted to the center console.

The correct set of staggered, two-piece ‘Style 2’ AMG wheels are presently shod in a set of Dunlop Sport Max tires. The stainless steel AMG exhaust system has been retained, and its appearance continues the SL 73’s understated aura which belies its overwhelming performance.